Roasted coffee is most flavorful when packaged immediately following the production process. It is desirable to package the coffee immediately after roasting and processing because contact between the coffee and ambient air can oxidize the coffee, causing a degradation in coffee flavor.
An obstacle to immediate packaging of the coffee is the well-known fact that roasted coffee produces large volumetric amounts of gas, including carbon dioxide gas. If the coffee is packaged in a flexible package, such as a pillow bag, the gas will cause the package to expand and to distort, potentially resulting in failure of the package or making the package appear swollen and unattractive to a consumer. The rate of gas production by the coffee can be decreased by degassing the coffee before packaging. However, degassing the coffee delays packaging and exposes the coffee to ambient air, potentially decreasing coffee flavor as described previously. And, a large building is required to accommodate the degassing equipment.
A solution to the aforementioned problems is to package the coffee immediately after roasting and processing in a package including a one-way pressure relief. A pressure relief valve provides an opportunity to release gas from the package while protecting the coffee from any contact with ambient air and the resultant oxidation. More specifically, the pressure relief valve is attached to, or is a part of, the coffee package. The pressure relief valve allows high-pressure gas out of the package while preventing ambient air from entering the package and coming into contact with the coffee.
For optimal valve operation, it is desirable for the pressure relief valve to be sensitive to increases in gas pressure within the package. Further, it is desirable for the valve to be engineered to both open and close consistently at known, predetermined pressures. Opening and closing at relatively lower pressures is desirable if the valve is to be used with a flexible package, such as a pillow bag, because the gas can be released before causing noticeable expansion and distortion of the bag.
Certain pressure relief valves utilize a component referred to in the valve industry as a “dry strap” or simply as a “strap” in combination with a fluid which wets a surface of the dry strap to control the one-way flow of gas through the valve. Such a dry strap is typically a strip-like layer or membrane which overlies a vent provided in a base or other element of the valve. The dry strap provides a closure around and over the vent which permits gas outflow while blocking ambient air inflow. The wetting fluid, such as a silicone oil, a graphite impregnated oil, or a food grade oil, is typically added between the dry strap and base or between the dry strap and other element and around the vent to wet the facing surface of the dry strap and base or other element facing the dry strap. The surface tension provided by the wetting fluid enables the dry strap to provide a complete closure of the dry strap against the base or other element of the valve, sealing the vent. The wetting fluid may be applied just before the valve is applied to the package or at the time of valve manufacture.
One-way pressure relief valves including a wetting fluid are excellent for their intended purpose. The wetting fluid provides for an excellent air-tight seal of the valve and valves including a wetting fluid can be engineered to open and close at predictable, low pressures.
However, the use of a wetting fluid introduces complexity to the valve manufacturing process. For example, inclusion of a wetting fluid requires a fluid-application step, which can add cost. If not manufactured correctly, it is possible that the wetting fluid can leak from the valve making the valve feel greasy and potentially diminishing the appearance of the valve to a consumer. If wetting fluid contacts the adhesive on the bottom of the valve prior to application, the wetting fluid can lessen the effectiveness of the adhesive.
It would be an improvement in the art to provide a one-way pressure relief valve which enables gas to be released from a package while blocking entry of ambient air or other gas back into the package, which is sensitive to gas pressure changes, which can be engineered to open and close reliably at known pressures, which, in certain embodiments, can be engineered to function with a wetting fluid and yet open and close at low pressures, which, in certain other embodiments, can be engineered to function without a wetting fluid and yet still open and close at low pressures, and which can contribute to a perceived improvement in the quality of the packaged goods.